Referring to FIG. 1, a conventional vacuum system includes: a closed housing 1; an ejector 3 mounted to the housing 1, and exhausting air from an inner space S of the housing 1; and a suction pad 4 communicating with the inner space S via a communicating hole 2 provided at a side of the housing 1. In a state where a surface of an object P comes into close contact with the pad 4, when the compressed air is discharged through the ejector 3, the air in both the housing 1 and the suction pad 4 is suctioned to the ejector 3 and discharged along with the compressed air.
In the process mentioned above, a vacuum is generated within the housing 1, and at the same time, a negative pressure is generated within the pad 4, whereby it is possible to grip the object P by means of the generated negative pressure. Here, when the communicating hole 2 is too large, a degree of vacuum may decrease; on the contrary, when the communicating hole 2 is too small, a vacuum speed may be reduced. Thus, a valve element is required so as to regulate the communicating hole 2.
As an example of a conventional valve, a valve 5 shown in FIG. 2, as a flexible member having an intake hole 6 that is narrower than the communicating hole 2, is provided on a bottom surface of the communicating hole 2 of the housing 1, and is locked by a piece 7. When the same ejector 3 is used, the smaller the size of the intake hole 6 can be and thus the slower the vacuum speed will be. On the contrary, the larger the size of the intake hole, the faster the vacuum speed will be.
Meanwhile, as shown in FIG. 1, it is preferred that the intake holes 6 of valves 5a and 5b, which are not used to grip the object P, are as small as possible or closed. Further, in the case where the object P is permeable, it is favorable that the vacuum speed is high in comparison with a case where the object is impermeable, so the intake hole 6 with a bigger aperture is required. In view of the examples described above, depending on the properties of the object P (material, weight, size, etc.), an optimum aperture of the intake hole 6 of the valve 5 varies.
However, the valve 5, which is described above, has a single intake hole 6, and accordingly has a vacuum characteristic thereof, and thus it is impossible to quickly and flexibly respond to various optimum apertures depending on the properties of the object P. To solve this problem, Korean Patent No. 10-0793323 discloses “Check-valve assembly for vacuum system”, which is invented by the inventor of the present invention.
FIG. 3 illustrates a valve assembly according to the related art mentioned above. The valve assembly 10 includes: a body 11 with a through-hole 12 at a side thereof; a shaft 13 rotatably mounted to the body 11; and a flexible valve 14 rotating along with the shaft by being locked to the shaft 13 and interfering with a lower portion of the through-hole 12. Here, the valve 14 is provided with a plurality of intake holes 15 and 16 having different sizes of apertures spaced apart from the shaft hole by a same radius of rotation.
In this structure, as the shaft 13 is rotated along with the valve 14, the through-hole 12 of the body 11 selectively communicates with one of the plurality of intake holes 15 and 16. In other words, the assembly 10 is advantageous in that the selection and change of the intake holes 15 and 16 of the valve are easy, and thus, it is possible to quickly respond to various optimum apertures depending on the properties of the object P.
However, in effect, in the valve assembly 10, the valve 14 is made of a thin and flexible rubber plate, so the valve assembly is disadvantageous in that deformation of the holes 15 and 16 may easily occur by exhaust pressure or vacuum pressure, and in the case where the hole is small, the holes may be clogged with particles, such as dust. Accordingly, it is impossible to design the hole to have various characteristics, such as the inner shape. Meanwhile, the valve is provided with a plurality of holes, whereby durability of the valve 14 decreases.
Consequently, the valve assembly 10 is not capable of regulating or controlling vacuum characteristics depending on the properties of the object P. In terms of structure, it is difficult to add the functional means for supplementing the control function above. Thus, the valve assembly 10 is rarely utilized on site.